I think for me, more often than not the IEM's are a good thing. But, the band I'm in now has a nice powered JBL system with a wedge for each of us. We're a 4 piece (acoustic, electric, bass and drum) and each of the guys has learned to play at the perfect volume (for me). Our drummer plays just hard enough and the guitar player gets just loud enough to cover his side of the stage and just a bit of mine. I actually have to turn him up in the wedge quite a bit to hear what he's got going on. We have a very clean wedge mix too. I get some of the acoustic and vox in mine and I'm good to go. I'm new to this band, but I don't have to push my rig near as much to get a good volume that also mixes with the band anything like any of my previous groups. I think the IE's can cover any situation but if you get a disciplined group of musicians together who think sonically and don't have to stroke their own egos, you can do fine with a non IEM rig. And we mix our own sound most of the time.